The endovascular treatment of a variety of maladies throughout the body is an increasingly more important form of therapy. One such procedure uses embolizing coils to occlude a target site by posing a physical barrier to blood flow and/or by promoting thrombus formation at the site. Such treatments can be useful where it is desired to reduce vascularization, including treatments for aneurysms and cancer.
Coils have typically been placed at a desired site within the vasculature using a catheter and a pusher. As a first step, a flexible, small diameter catheter can be guided to the target site through the use of delivery wires or by flow-directed means such as balloons placed at the distal end of the catheter. Once the site has been reached, the catheter lumen is cleared by removing the delivery wire (if a delivery wire has been used), and the coil is placed into the proximal open end of the catheter and advanced through the catheter with a pusher. Pushers are wires having a distal end that is adapted to engage and push the coil through the catheter lumen as the pusher is advanced through the catheter. When the coil reaches the distal end of the catheter, it is discharged from the catheter by the delivery wire into the vascular site.
Several techniques have been developed to enable more accurate placement of coils within a vessel. In one technique the coil is bonded via a metal-to-metal joint to the distal end of the pusher. The pusher and coil are made of dissimilar metals. The coil-carrying pusher is advanced through the catheter to an anatomic site and a small electrical current is passed through the pusher-coil assembly. The current causes the joint between the pusher and the coil to be severed via electrolysis. The pusher may then be retracted leaving the detached coil at a target position within the vessel. In addition to enabling accurate coil placement, the electric current may facilitate thrombus formation at the coil site. A perceived disadvantage of this method is that the electrolytic release of the coil requires a period of time so that rapid detachment of the coil from the pusher does not occur.
Another technique for detaching an embolic coil uses a mechanical connection between the coil and the pusher. For example, one such device uses interlocking clasps which are secured to each other by a control wire that extends the length of the catheter. Retraction of the control wire uncouples the coil from the pusher. While mechanical connections between coils and pusher wires provide for quick detachment, such detachable coils require additional control mechanisms (i.e., control wires) to deploy the coil.
Accordingly, while conventional systems provide effective coil delivery, further improvements that facilitate delivery, while reducing the chance of premature deployment or jamming, would be beneficial.